1. Field of the Invention
The present invention relates to improvements in electrographic development structures, procedures and systems (i.e. cooperative developer/applicator combinations) and more particularly to such improvements for development with electrographic developer containing hard magnetic carrier and electrically insulative toner.
2. Description of the Prior Art
U.S. application Ser. No. 440,146, filed Nov. 8, 1982, now abandoned, in the names of Miskinis and Jadwin, discloses a "Two-Component, Dry Electrographic Developer Compositions Containing Hard Magnetic Carrier and Method for Using the Same". In general, the system disclosed in that application employs, in combination with a magnetic brush applicator that comprises a magnetic core which rotates within a nonmagnetic shell, a developer mixture that comprises electrically insulative toner particles and "hard" magnetic carrier particles (which exhibit a high minimum level of coercivity when magnetically saturated). The toner and carrier particles obtain an opposite triboelectric charge by mixing interactions. This applicator-developer system provides important electrographic development improvements, for example in increasing development rates, in reducing scratches in the developed image and in reducing developed image patterns that are caused by defects of the magnetic field pattern.
In continuing development work with applicator-developer systems such as described in the above-cited application, we have encountered several difficulties. For example, in some circumstances there occur unwanted density variations in background that are related to other solid-area image portions. Also, it has been noted that with some embodiments of the above-described system undesirable amounts of picked-up carrier particles are present in the developed image.
Further, we have discovered that there are some particularly preferred means and methods for implementing the development approach that is taught in the Miskinis and Jadwin application and that such preferred means and methods provide enhanced development results, e.g. from the combined viewpoints of (1) development completeness for solid area edges, fineline images and half-tone dots and (2) for uniformity and smoothness of image development.